This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-340844, filed Nov. 6, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a light-receiving element, a light-receiving element array prepared by arranging a plurality of light-receiving elements, and a light-receiving module using the light-receiving element array.
2. Description of the Related Art
Conventionally, a planar light-receiving element using a semiconductor is known as a light-receiving element. The planar light-receiving element is represented as a xe2x80x9clight-receiving elementxe2x80x9d in the specification. The conventional light-receiving element is constructed as described below.
An electrode on the negative side, which is referred to as a xe2x80x9ccathodexe2x80x9d herein later, is formed on one surface of a semiconductor substrate. On the other hand, a buffer layer (an InP layer, etc.), an absorption layer (an InGaAs layer, etc.), an (InP) window layer, a protective film and an electrode on the positive side, which is referred to as an xe2x80x9canodexe2x80x9d herein later, are formed one by one on the other surface of the semiconductor substrate. The anode, which has an annular electrode (referred to as a xe2x80x9cring electrodexe2x80x9d, hereinafter), is connected to a pad electrode. The light incident from the light-receiving surface of the ring electrode is absorbed by the absorbing layer and is converted into an electric signal.
In the light-receiving element of the configuration described above, since a parasitic capacitance caused by the MIS (Metal-Insulator Semiconductor) structure is appeared in the pad electrode region, the capacitance of the entire light-receiving element increases. The increase in the capacitance of the light-receiving element gives rise to the problem that the response characteristics are lowered in, particularly, the high frequency region. Further, in a case that a load applied to the pad electrode is large in the bonding step, there is also a problem that the surface leakage current increases by breaking the protective film.
An object of the present invention is to provide a light-receiving element, a light-receiving array and a light-receiving module whose response characteristics is improved and the surface leakage current is suppressed even in a case where the protective film is broken by the load applied to the pad electrode in the bonding step and to provide method for providing a light-receiving element having the high frequency characteristics.
To achieve above-mentioned object, the following means are measured.
A light-receiving element according to the first aspect of the present invention is characterized by comprising: an absorption layer formed on a semiconductor substrate; a window layer formed on the absorption layer; a first electrode formed on the window layer; a second electrode formed on the window layer and electrically connected to the first electrode; and a diffusion region being formed in the absorption layer and the window layer, the diffusion region being formed between the first electrode and the substrate and between the second electrode and the substrate. With this configuration, it is preferable a dielectric layer is formed between the diffusion layer and the second electrode.
A light-receiving element according to the second aspect of the present invention is characterized by comprising: an absorption layer formed on a semiconductor substrate; a window layer formed on the absorption layer; a first electrode formed on the window layer; a second electrode formed on the window layer and electrically connected to the first electrode; a diffusion layer being formed in the absorption layer and the window layer, the diffusion layer being formed between the first electrode and the substrate; and a dielectric layer formed between the window layer and the second electrode. With this configuration, it is preferable the diffusion layer is also formed between the dielectric layer and the substrate.
Preferable modes of the light-receiving element according to the first and second aspects are as follows.
(1) The semiconductor substrate is an n-type substrate. It is preferable that the substrate is made of InP or Si.
(2) The first electrode is a positive electrode (anode) and a ring electrode.
(3) The second electrode is a pad electrode.
(4) The window layer is an n-type layer.
(5) A thickness of the absorption layer is no less than 3 xcexcm. It is preferable that the thickness of the absorption layer is 6 xcexcm.
(6) The diffusion layer is light-receiving region in which Zn is diffused.
(7) A third electrode formed on a surface on which the absorption layer is not formed is further provided, and the third electrode comprises an opening for passing the light transmitted through the absorption layer.
(8) The third electrode is a negative electrode (cathode).
(9) A protective film formed on the window layer is further provided.
(10) The first electrode is connected to the window layer by penetrating the protective film.
(11) A cap layer (InGaAs, InGaP) formed between the window layer and the first electrode is further provided.
(12) In (11), the cap layer is formed apart form the protective layer formed on the window layer.
(13) The dielectric layer is made of SiO2 or SiN or a stacked layer thereof.
(14) A cutoff frequency is equal to or more than 3 GHz in a case that the bias voltage is 1 V, or a cutoff frequency is equal to or more than 2.5 GHz in a case that the bias voltage is 0.5 V.
A light-receiving element array according to the third aspect of the present invention is characterized in that plurality of above-mentioned light-receiving elements are arranged to form an array, and is characterized by further comprising a trench formed between the adjacent light-receiving elements in a manner to extend to reach a position where the absorption layers are separated from each other.
A light-receiving module according to the fourth aspect of the present invention is characterized by comprising: the above-mentioned optical bench; and a package having an electrical wiring electrically connected to the light-receiving element, to fix the optical bench.
A method for manufacturing a light-receiving element according to the fifth aspect of the present invention is characterized by comprising: forming an absorption layer formed on a semiconductor substrate; forming a window layer formed on the absorption layer; forming a first electrode formed on the window layer; forming a second electrode formed on the window layer and electrically connected to the first electrode; and forming a diffusion region being formed in the absorption layer and the window layer, the diffusion region being formed between the first electrode and the substrate and between the second electrode and the substrate.
A method for manufacturing a light-receiving element according to the sixth aspect of the present invention is characterized by comprising: forming an absorption layer formed on a semiconductor substrate; forming a window layer formed on the absorption layer; forming a first electrode formed on the window layer; forming a second electrode formed on the window layer and electrically connected to the first electrode; forming a diffusion layer being formed in the absorption layer and the window layer, the diffusion layer being formed between the first electrode and the substrate; and forming a dielectric layer formed between the window layer and the second electrode.
A method for manufacturing a light-receiving element according to the seventh aspect of the present invention is characterized by comprising: step for forming an absorption layer formed on a semiconductor substrate; step for forming a window layer formed on the absorption layer; step for forming a first electrode formed on the window layer; step for forming a second electrode formed on the window layer and electrically connected to the first electrode; and step for forming a diffusion region being formed in the absorption layer and the window layer, the diffusion region being formed between the first electrode and the substrate and between the second electrode and the substrate.
A method for manufacturing a light-receiving element according to the eighth aspect of the present invention is characterized by comprising: step for forming an absorption layer formed on a semiconductor substrate; step for forming a window layer formed on the absorption layer; step for forming a first electrode formed on the window layer; step for forming a second electrode formed on the window layer and electrically connected to the first electrode; step for forming a diffusion layer being formed in the absorption layer and the window layer, the diffusion layer being formed between the first electrode and the substrate; and step for forming a dielectric layer formed between the window layer and the second electrode.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.